Document that expressions in non-trailing expression statements without semicolon must have type `()`

[petrochenkov]

cc rust-lang/rust#61753

[ehuss]

Can you say more about what is missing? In https://doc.rust-lang.org/nightly/reference/statements.html#expression-statements it says:

The type of ExpressionWithBlock expressions when used as statements must be the unit type.

And here "ExpressionWithBlock" means an expression statement without a semicolon. It's not explicit about whether or not it is "trailing" because a block expression defines the trailing expression as "ExpressionWithoutBlock".

It seems to be essentially what you are asking for?

[petrochenkov]

Nice!
Didn't found that.

That paragraph covers this issue, except that the code example is not good:

// if true {
//   1
// }

That's a type mismatch between if and (implicit) else results, not the mismatch with the () expected from non-trailing expression statements.